Two-piece rotary metal-cutting tool and method for interconnecting the pieces

ABSTRACT

A tool includes a tool body and a cutting portion detachably mounted thereon, the tool being rotatable about a longitudinal center axis. The tool body includes flutes formed in an outer surface thereof, and a pair of forward projections at a front end thereof. The cutting portion includes front flutes formed in an external side thereof, and a pair of recesses extending circumferentially in communication with respective ones of the front flutes. To connect the cutting portion to the tool body, the cutting portion and tool body are converged longitudinally so that the projections enter the front flutes. Then, relative rotation is produced between the cutting portion and tool body to align the front flutes with the rear flutes while causing the projections to enter the recesses and form therewith a bayonet coupling.

[0001] This application is a continuation of application Ser. No.08/929,462, filed Sep. 15, 1997.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to a tool for rotary, cuttingmachining, comprising a tool body and a cutting portion. The tool bodyhas a front surface, and the cutting portion has a support surfaceprovided to releaseably abut against the front surface in asubstantially radial plane. The tool body and the cutting portioncomprises means which cooperate for holding them together. The inventionalso relates to a cutting portion and a tool body as well as a methodfor mounting a cutting portion to a tool body.

PRIOR ART

[0003] It is previously known to use interchangeable cutting edges ondifferent types of tools for cutting machining, especially when cuttinga metallic workpiece. This technique however has practical limitationsdue to handling reasons when it comes to milling and drilling toolswhich rotate around a longitudinal axis.

[0004] Through DE-PS-367,010 and Burger U.S. Pat. No. 2,259,611, it ispreviously known to provide drills with lockable drill tips, wherein thedrill tip is retained with the aid of dove-tail profiles or with pressfit, respectively. The known tools however are impaired with drawbackssuch as bad torsion transferring ability and troublesome mounting anddismounting.

[0005] The present invention has as one object to provide drilling andmilling tools with interchangeable cutting edges, which eliminatesproblems associated with known techniques.

[0006] Another object with the present invention is provide a rigid toolpreferably for drilling or milling wherein the cutting portioncooperates with the tool body via a bayonet coupling.

[0007] Another object of the present invention is to provide a rigidtool preferably for drilling or milling wherein the cutting portion canbe easily exchanged by hand without time consuming screwing orsoldering.

[0008] Another object of the present invention is to provide a tool witha self centering cutting portion.

SUMMARY OF THE INVENTION

[0009] These and other objects have been achieved by the presentinvention which relates to a rotary metal-cutting tool comprising, incombination, a tool body and a cutting portion attached to the toolbody. The tool body includes a shank portion defining a longitudinalcenter axis, a front surface, and rear chip flutes formed in an externalside surface of the shank portion for guiding chips rearwardly during acutting operation. The cutting portion includes a rear support surfaceabutting the front surface, a front cutting face, and front chip flutesformed in a side surface of the cutting portion and intersecting thecutting face to form cutting edges therewith. The tool body and cuttingportion are interconnected by a bayonet coupling formed by projectionsdisposed on one of the tool body and cutting portion, and recessesformed in the other of the tool body and cutting portion. Theprojections are circumferentially offset with respect to the flutes andextend generally longitudinally. The recesses extend circumferentiallyfrom respective flutes. The flutes are sized to longitudinally receiverespective projections during longitudinal insertion or removal of thecutting portion relative to the tool body. The cutting portion isrotatable about the center axis relative to the tool body to transferthe projections from the respective flutes and into the recesses whilebringing the front flutes into alignment with the rear flutes.

[0010] The invention also relates to a method of mounting a cuttingportion to a tool body to form a metal-cutting rotary tool. The toolbody includes a shank portion, a front surface, and rear chip flutesformed in an outer surface of the tool body. The cutting portionincludes a support surface abutting the front surface, a cutting surfacehaving cutting edges, and front chip flutes formed in an outer surfaceof the cutting portion. One of the tool body and cutting portionincludes longitudinal projections, and the other of the tool body andthe cutting portion includes circumferential recesses. Each recesscommunicates with a respective flute and extends less than 180°. Themethod comprises the steps of:

[0011] A) converging the cutting portion and tool body longitudinallytoward one another to bring the projections into respective ones of theflutes that communicate with the circumferential recesses; and

[0012] B) effecting relative rotation between the tool body and cuttingportion to cause the projections to enter respective ones of therecesses to bring the front flutes into alignment with the rear flutesand to bring a stop surface of each projection into longitudinallyopposing relationship with a stop surface of a respective recess fordefining a bayonet connection preventing longitudinal displacement ofthe cutting portion relative to the tool body.

DESCRIPTION OF THE DRAWINGS

[0013] The objects and advantages of the invention will become apparentfrom the following detailed description of a preferred embodimentthereof in connection with the accompanying drawing in which likenumerals designate like elements, and in which:

[0014]FIG. 1 shows a drilling tool according to the present invention,in an exploded perspective view;

[0015]FIG. 2 shows a cutting portion according to the present inventionin a bottom view;

[0016]FIG. 3 shows the cutting portion in a sectional view taken alongthe line III-III in FIG. 2;

[0017]FIG. 3A shows the cutting portion in a perspective view frombelow;

[0018]FIG. 4 shows the forward end surface of a tool body according tothe present invention in top view;

[0019]FIG. 5 shows the drill shank in a sectional view taken along theline V-V in FIG. 4;

[0020]FIGS. 6, 7 and 8 show cross-sections of a bayonet coupling of thetool;

[0021]FIG. 9 shows the assembled tool according to FIG. 1 in a magnifiedside view.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

[0022] The embodiment of a tool 10 according to the invention shown inFIG. 1 is a so called helix drill, which comprises a cutting portion ordrill tip 11 and a drill body 12. The drill has a rotational directionR.

[0023] The drill tip 11 is provided with at least one cutting edge 19 inthe forward end thereof facing away from the drill body 12, which tip isgiven different designs depending on the area of application.

[0024] The drill tip 11 is made of hard material, preferably cementedcarbide and most preferably of injection molded cemented carbide, andcomprises a front cutting surface formed by two upper clearance faces15, a lower support surface 16 as well as first and second curvedsurfaces 41, 18 interconnecting the surfaces 15 and 16. All thesesurfaces and associated edges are integrated as one piece with the drilltip and consequently formed of the same material, i.e. preferablyinjection molded cemented carbide. The curved surfaces 18 form frontchip flutes for conducting cuttings rearwardly. Lines of intersectionbetween the chip flutes 18 and the clearance faces 15 form main cuttingedges 19, preferably via reinforcing chambers, not shown. Lines ofintersection between the first curved surfaces 41 and the chip flutes 18form secondary cutting edges 19′. The chip flute is shown as helical butmay alternatively be adapted for a drill body requiring straight chipflutes. The radially external parts between the chip flutes consist ofprotruding lands formed by the surfaces 41, each having acircumferential length G (FIG. 4). The largest diameter of the drill tipis the diametrical distance between the radially extreme points of thesecondary cutting edges. The height of the drill tip is substantiallythe same as the largest diameter of the tip, in order to minimize thewear from chips on the joint between the drill tip and the drill body.Flushing holes 23, extending substantially parallel with the rotationalaxis 22, extend through the drill tip from the support surface 16 to theorifice in respective upper clearance surface 15.

[0025] The support surface 16 according to FIGS. 2, 3 and 3A issubstantially planar but comprises a recess 50 at the transition betweenthe support surface 16 and the land 41. Each recess 50 comprises a firstfree or end surface 51 perpendicularly connected to both the land 41 anda second free surface 52 (see FIG. 8), which surface 52 in turn forms anacute angle a with a first guiding surface 53 (see FIG. 6). The surface53 connects to a second guiding surface 54 oriented parallel to therotational axis 22, and which connects to the support surface 16 via aradius or an entering bevel 55. The surface 53 is inclined obliquelyrelative to the center axis 22 so as to face generally radially inwardlyand longitudinally rearwardly. As illustrated in FIG. 3, support surface16, recesses 50, and land 41 define a generally dovetail-shapedprojection. The recess 50 has a stop surface 56 (FIG. 3A) which isparallel to the axis 22 and which suitably lies in an axial plane whichintersects said axis. The recess 50 extends in a tangential directionfrom the chip flute 18 to about a midpoint of the circumferential lengthG of the associated land 41.

[0026] The drill body is made of a material which has a lower Young'smodulus than cemented carbide. The drill body has helical rear chipflutes 18A (or straight chip flutes if required) and these can extendalong the entire outer surface of a shank portion 40 of the body oralong only a part thereof. The drill body 12 is provided with a frontsurface 24 at the end facing towards the drill tip 11, which surface 24abuts against the support surface 16 of the drill tip 11. The largestdiameter of the support surface 16 is larger than the largest diameterof the front surface 24 in order to minimize the wear from chips on thejoint between the drill tip and the drill body. The drill body alsoincludes curved surfaces 41A forming lands. The front surface 24 issubstantially planar but comprises a projection 60 at the transitionbetween the front surface 24 and the jacket surface of each land 41A.The height of the projection is somewhat less than that of the depth ofthe recess 50.

[0027] Each projection 60 comprises a first free or end surface 61perpendicularly connected to the jacket surface 41A, said surface 61also perpendicularly connected to a second free surface 62, which in itsturn forms an acute angle π with a first guiding surface 63. The surface63 connects to a second guiding surface 64 oriented parallel to therotational axis 22. The surface 64 connects to the front surface 24 viaa radius 65. The surface 63 is oriented parallel to the surface 53 so asto face generally radially outwardly and longitudinally forwardly. Asillustrated in FIG. 5, the above-described surfaces, along with frontsurface 24, form a centrally disposed generally dovetail-shaped recess.The projection 60 has a stop surface 66, FIG. 9, which is parallel withthe axis 22 and which suitably lies in an axial plane which containssaid axis.

[0028] The smallest diameter of the front surface 24 is smaller than thelargest diameter of the drill tip but larger than the smallest diameterof the drill tip. The projection 60 extends in a tangential directionfrom the chip flute 18A to about the midpoint of the circumferentialtangential length G′ of the associated land 41A.

[0029] The stop surfaces 56 and 66, respectively, should be as far fromthe rotational axis as possible for best moment transfer, i.e. they arearranged diametrically opposed each other. The drill tip must besymmetrically formed in order to retain the tool's concentricity atvarying strain, i.e. in order to keep the drill tip centered relative tothe drill body. The projections 60 and the recesses 50 lie at a distancefrom and substantially rearwardly of the associated cutting edge 19 inthe tool's rotational direction R.

[0030] Mounting of the drill tip 11 on the drill body 12 is done asfollows. The drill tip 11 is brought in the axial direction towards thedrill body 12, so that each projection 60 is received in the associatedchip flute 18 and so that the support surface 16 abuts against the frontsurface 24 thereby bringing the generally dove-tail shaped projection ofthe drill tip 11 into mating engagement with the generallydovetail-shaped recess of drill body 12. Then, the drill tip is rotatedin the direction R within an angle interval φ which is less than 360°,preferably less than 60°, relative to the drill body so that eachprojection 60 moves with a slide fit in the respective recess 50 untilthe stop surfaces 56 and 66 abut against each other. The drill tip 11 isnow anchored in the drill body 12 in a satisfactory manner. Thus, thepreformed spaces defined by the chip flutes 18 are used as the entranceand the exit of the bayonet coupling.

[0031] When the drill tip 11 must be replaced, the mounting procedure isreversed. The drill tip 11 then can be removed from the drill body 12and be exchanged, preferably with the aid of a suitable key inengagement with the chip flutes on the drill tip. The key is preferablyalso used during mounting of the drill tip.

[0032] The surfaces which during the drilling operation must be inengagement are surfaces 53 and 63 as well as the support surface 16 andthe front surface 24. The surfaces 53 and 63 cooperate to hold the drilltip such that it cannot loosen in the feed direction, for example duringretraction of the tool. The surfaces 53 and 63 are preferably designedsuch that their cooperation results in some elastic deflection of theprojection 60 due to the slide fit. A limited contact surface betweensurfaces 54 and 64 can be allowed, but this implies an increased momentat the radius 65. The drill tip is self-centering in the tool body, i.e.it moves such that its axis coincides with the rotational axis 22 if ithas been displaced during the machining operation. The surface 55 willallow the radius 65 of the tool body to be relatively large. Thesurfaces 52 and 62 should not be in engagement with each other duringthe machining operation. That is realized by extending the surface 53(see FIG. 6). The clearance surfaces 51 and 61 should not be inengagement with each other during the machining operation, and thereforea gap P is always present between them (see FIG. 6). The gap P is in therange of 0.1-1.0 mm. The support surface 16 will be pressed by the feedforce against the front surface 24 during the machining operation, whichmeans that the elastic deflection of the projection 60 tends to decreasesomewhat, which however is counteracted because the projection 60 willbe bent radially inwardly due to pressure on the front surface 24 fromthe feed force.

[0033] The invention is useable also for milling cutters. The drill tipis preferably coated with layers of, for example, Al₂O₃, TiN and/orTiCN. In certain cases, it can be well-founded to apply super hardmaterial such as CBN or PCD on the cutting edges. Alternatively ceramicmaterial can be used at injection molding of the drill tips.

[0034] Although the present invention has been described in connectionwith a preferred embodiment thereof, it will be appreciated by thoseskilled in the art that additions, modifications, substitutions anddeletions not specifically described may be made without departing fromthe spirit and scope of the invention as defined by the appended claims.

What is claimed is:
 1. A rotary metal-cutting tool comprising, incombination, a tool body and a cutting portion attached to the toolbody; the tool body including: a shank portion defining a longitudinalcenter axis, a front surface, and rear chip flutes formed in an externalside surface of the shank for guiding chips rearwardly during a cuttingoperation; the cutting portion including: a rear support surfaceabutting the front surface, a front cutting surface, and front chipflutes formed in a side surface of the cutting portion and intersectingthe cutting face to form cutting edges therewith; the tool body andcutting portion being interconnected by a dovetail-shaped bayonetcoupling formed by projections disposed on one of the tool body andcutting portion, and recesses formed in the other of the tool body andcutting portion, the projections being circumferentially offset withrespect to the flutes and extending generally longitudinally; therecesses extending circumferentially from respective flutes; the flutessized to longitudinally receive respective projections duringlongitudinal insertion or removal of the cutting portion relative to thetool body; the cutting portion being rotatable about the center axisrelative to the tool body to transfer the projections from therespective flutes into the recesses while bringing the front and rearflutes into mutual alignment.
 2. The tool according to claim 1 whereinthe recesses are formed in the cutting portion; and the projections areformed in the tool body.
 3. The tool according to claim 1 wherein therecesses are formed in the outer surface of the cutting portion; thecutting portion being rotatable relative to the tool body by an angleless than 360 degrees.
 4. The tool according to claim 3 wherein theangle is less than 60 degrees.
 5. The tool according to claim 1 whereineach of the projections includes a first surface inclined obliquelyrelative to the center axis, the first surface facing generally radiallyinwardly and longitudinally rearwardly; each of the recesses including asecond surface inclined obliquely relative to the center axis, thesecond surface facing generally radially outwardly and longitudinallyforwardly and opposing a respective first surface to prevent relativelongitudinal movement of the cutting portion relative to the tool body.6. The tool according to claim 5 wherein a material from which the toolbody is formed has a lower Young's modulus than a material from whichthe cutting portion is formed, to enable the projections to bendelastically in a radial direction during relative rotation between thecutting portion and tool body.
 7. The tool according to claim 1 whereineach of the projections includes a first surface inclined obliquelyrelative to the center axis, the first surface facing generally radiallyinwardly and longitudinally rearwardly; each of the recesses including asecond surface inclined obliquely relative to the center axis, thesecond surface facing generally radially outwardly and longitudinallyforwardly and opposing a respective first surface to prevent relativelongitudinal movement of the cutting portion relative to the tool body.8. The tool according to claim 6 wherein the outer surface of thecutting portion defines a pair of lands extending circumferentially byequal distances between the front flutes, each of the recesses extendingcircumferentially for a distance of about one-half of thecircumferential distance of a respective land, each of the projectionsextending circumferentially a distance substantially equal to that of arespective recess.
 9. The tool according to claim 1 wherein each of theprojections includes a first surface inclined obliquely relative to thecenter axis, the first surface facing generally radially inwardly andlongitudinally rearwardly; each of the recesses including a secondsurface inclined obliquely relative to the center axis, the secondsurface facing generally radially outwardly and longitudinally forwardlyand opposing a respective first surface to prevent relative longitudinalmovement of the cutting portion relative to the tool body.
 10. The toolaccording to claim 1 wherein each of the projections includes aforwardly facing end surface, and the recess includes a forwardly facingend surface, and the recess includes a rearwardly facing end surfacespaced from the forwardly facing end surface by a gap.
 11. A cuttingportion adapted to be connected to a tool body for rotary metal cutting,comprising a front cutting surface having at least one cutting edge, arear support surface, and at least one chip flute formed in a sidesurface of the cutting portion for guiding cuttings, said cuttingportion including coupling means defining a dovetail-shaped projectionand forming part of a bayonet coupling adapted to connect a tool bodywith the cutting portion.
 12. The cutting portion according to claim 11wherein the coupling means comprises a recess extendingcircumferentially less than 60 degrees.
 13. A rotary drill comprising: adrill body having a longitudinal axis and first and second opposed ends,one of said opposed ends comprising a centrally disposed dovetail-shapedrecess, and at least two circumferentially spaced projections, each ofsaid projections having a stop surface; a replaceable drilling headhaving first and second opposed ends, one of said opposed endscomprising a cutting portion, and the other of said opposed endscomprising a dovetail-shaped projection, said drilling head furthercomprising at least one stop surface.
 14. A method of attaching adrilling head to a drill body, said drill body having a longitudinalaxis and first and second opposed ends, one of said opposed endscomprising a centrally disposed dovetail-shaped recess, and at least twocircumferentially spaced projections, each of said projections having astop surface; said drilling head having first and second opposed ends,one of said opposed ends comprising a cutting portion, and the other ofsaid opposed ends comprising a dovetail-shaped projection, said drillinghead further comprising at least one stop surface; wherein said methodcomprises: inserting said dovetail-shaped projection into saiddovetail-shaped recess; and rotating said drilling head relative to saiddrill body such that the at least one stop surface on said drilling headcomes into engagement with at least one of the stop surfaces on one ofthe projections.
 15. A method for mounting a cutting portion to a toolbody to form a metal-cutting rotary tool, the tool body including ashank portion; a front surface, and rear chip flutes formed in an outersurface of the tool body; the cutting portion including a supportsurface abutting the front surface, a cutting surface having cuttingedges, and front chip flutes formed in an outer surface of the cuttingportion; one of the tool body and cutting portion including longitudinalprojections, and the other of the tool body and cutting portionincluding circumferential recesses, each recess communicating with arespective flute and extending less than 180 degrees; the methodcomprising the steps of: A) converging the cutting portion and tool bodylongitudinally toward one another to bring the projections intorespective ones of the flutes that communicate with the circumferentialrecesses; and B) effecting relative rotation between the tool body andcutting portion to cause the projections to enter respective ones of therecesses to bring the front flutes into alignment with the rear flutes,and to bring a stop surface of each projection into longitudinallyopposing relationship with a stop surface of a respective recess fordefining a dovetail-shaped bayonet connection preventing longitudinaldisplacement of the cutting portion relative to the tool body.